1. Field of the Invention
The present invention relates to the detection of glucose in samples which may also contain potential interfering compounds, such as α-hydroxy acids or β-diketones.
2. Description of the Related Art
The complexation of carbohydrates, including glucose, with phenylboronic acid has been known for a long time and the reversibility of that interaction has served as a basis for the chromatographic separation of sugars. Specifically, in 1959, Lorand and Edwards reported association constants for aqueous associations of phenylboronic acid with many saturated polyols; binding interactions ranged from very weak (e.g., ethylene glycol, Kd=360 mM) to moderately strong (e.g., glucose, Kd=9.1 mM). See J. Yoon, et al., Bioorganic and Medicinal Chemistry 1 (4):267–71 (1993). The binding mechanism is believed to occur through bonding of adjacent hydroxyl groups on glucose to hydroxyl groups on a boronate moiety.
U.S. Pat. No. 5,503,770 (James, et al.) describes a fluorescent boronic acid-containing compound that emits fluorescence of a high intensity upon binding to saccharides, including glucose. The fluorescent compound has a molecular structure comprising a fluorophore, at least one phenylboronic acid moiety and at least one amine-providing nitrogen atom where the nitrogen atom is disposed in the vicinity of the phenylboronic acid moiety so as to interact intramolecularly with the boronic acid. Such interaction thereby causes the compound to emit fluorescence upon saccharide binding. See also T. James, et al., J. Am. Chem. Soc. 117 (35):8982–87 (1995).
Additionally, fluorescent sensors using an anthrylboronic acid-containing compound for detecting blood glucose are known in the art. For example, J. Yoon, et al., J. Am. Chem. Soc. 114:5874–5875 (1992) describe that anthrylboronic acid can be used as a fluorescent chemosensor for signaling carbohydrate binding, including binding of glucose and fructose.
Unfortunately, compounds which interact with glucose in the manner described above also have a tendency to interact with other compounds having hydroxyl groups, thus reducing the specificity of a glucose assay, especially when assaying physiological samples which may contain interfering amounts of lactate, acetoacetate, etc. For example, some diabetic patients also develop lactic acidosis, in which blood lactate levels are greater than 5 mmol/liter. Thus, there remains a great need for glucose assays which are relatively insensitive to potentially interfering hydroxyl compounds, such as lactate.